Japan's prime minister vowed Sunday to seek talks with Pyongyang in a bid to settle the nagging issue of North Korea's kidnapping of Japanese, without risking its alliance with Washington and Seoul.

Shinzo Abe made the comment after a surprise visit to North Korea by one of his advisers last week has irritated the United States and South Korea as a possible damper to their efforts to forge a united front against Pyongyang.

"I want to pursue negotiations or dialogue" with North Korea, he told reporters in Fukuoka, southern Japan, according to Japanese media.

"I will definitely try to realise the return home of all the kidnap victims, the search for truth behind the cases and the handover of the abductors during the Abe government," he said.

But he added Japan will also continue seeking a "comprehensive solution" to the abduction issue along with North Korea's nuclear and missile ambitions in concerted efforts with allies.

The adviser, Isao Iijima, returned home via Beijing on Saturday after the four-day visit to Pyongyang where he discussed with North Korean officials ways to resolve the long-pending abduction issue, which has derailed bilateral talks to improve ties.

Iijima told North Korean officials that Tokyo "would not make any move" unless they return all Japanese kidnap victims, hand over the kidnappers and resolve all the abduction cases, according to Japanese media citing sources close to him.

But the trip has fuelled speculation Pyongyang was trying to cozy up to Tokyo at a time when ties with Washington and Seoul have gone into deep freeze over its nuclear and missile ambitions.

South Korea dubbed the trip "unhelpful" to international efforts to forge a united front against Pyongyang.

Glyn Davies, the US special representative for North Korea policy, initially expressed surprise on Tuesday by saying Iijima's trip was "news" to him.

Davies was visiting Seoul, the first leg of his tour which later took him to Beijing and Tokyo for talks with government officials there.

"We knew that North Korea would eventually shift their strategy to that of seeking engagement in an effort to split us and to exploit any differences in our respective national positions," Davies told reporters on Saturday at the end of his stay in Tokyo.

Davies, however, said he was confident Tokyo was "fully aware of the challenges and pitfalls of engaging North Korea."

A member of Abe's cabinet on Sunday defended Iijima's trip which he said reflected the premier's resolve to have North Korea come clean on the abductions which took place in the 1970s and 1980s.

"Japan has an extremely important case, the abduction issue, which is separate from interests of other countries," Akira Amari, the state minister of economic revitalisation, said in a talk show on public broadcaster NHK.

"This is an area in which Japan should act on its own initiative," he added.

In 2002, North Korea officially admitted to the abductions but its refusal to give a fuller account of the cases has infuriated Japan.

Iijima was a senior aide to Junichiro Koizumi and accompanied his visits to Pyongyang in 2002 and 2004 as Japan's prime minister for talks with then-North Korean leader Kim Jong-Il.

During Koizumi's 2002 trip, North Korea admitted its agents kidnapped Japanese nationals in Cold War years to train spies in Japanese language and customs.

Several of those snatched were allowed to return to Japan along with children who were born in the North, but Pyongyang said the rest of them had died, although many in Japan were not convinced.